The permanent alteration of the color of keratinous fibers, in particular human hair, by the application of hair dyes is well known. In order to provide the consumer with the hair color and the intensity of color desired, a very complex chemical process is utilized. Permanent hair dyeing formulations typically comprise developers (also known as oxidative hair dye precursors or primary intermediates) and couplers (also known as color modifiers or secondary intermediates). Developers are sufficiently small to diffuse into the hair shaft where, once activated by an oxidizing agent, such as hydrogen peroxide, the developers react with other dye compounds, e.g., couplers, to form larger colored complexes, chromophores, in the hair shaft. Couplers, which are also sufficiently small to diffuse into the hair shaft, are generally colorless molecules that form colors in the presence of activated developers. Developers can be used alone or in combination with other developers, and one or more can be used in combination with one or more couplers.
Hair colorant products are typically sold in the form of kits containing a dye component, e.g., a dye lotion, and an oxidizing component, e.g., a hydrogen peroxide solution. The dye component typically has developers (also known as oxidative hair dye precursors or primary intermediates) and couplers (also known as color modifiers or secondary intermediates). In use, the dye component is mixed with the oxidizing component and the resultant mixture is applied to the hair. Developers are sufficiently small to diffuse into the hair shaft where, once activated by an oxidizing agent, such as hydrogen peroxide, the developers react with other dye compounds, e.g., couplers, to form larger colored complexes, chromophores in the hair shaft. Couplers, which are also sufficiently small to diffuse into the hair shaft, are generally colorless molecules that form colors in the presence of activated developers. When the dye component and the oxidizing component are mixed, oxidizing agent present in the oxidizing component begins to oxidize developers present in the dye component and the oxidized developers begin to react with couplers to form chromophores. Thus, some fraction of chromophores is formed outside of the hair fibers, e.g., in the mixing container, before the mixture is applied to the hair. The chromophores formed in the hair shaft do not readily diffuse out of the hair during subsequent washing with water and/or detergents and thereby give the colorant benefit desired by consumers.
When oxidation of the developers takes place outside of the hair, in the mixing container, the dyeing power of the colorant composition (dyeing composition and oxidant composition combined together) gradually decreases and it can become more difficult to achieve a uniform color on the head (between the time when the dyeing composition is applied to the first lock of hair to the time when the dyeing composition is applied to the last lock treated, the dyeing composition is completely oxidized). Inhibiting oxidation of the developers outside of the hair improves dye efficiency, by reducing the premature consumption of dye intermediates. Finally, when oxidation of the developers outside of the hair is inhibited, the color generated by the colorant composition is more reproducible, from user to user. It is therefore desirable that a colorant composition does not form color outside of the hair fiber.
Attempts have been made to inhibit the oxidation of developers outside of the hair and thereby inhibit color formation outside of the hair. For example, 1-phenyl-3-methyl-5-pyrazolone is known to the hair color industry as an antioxidant that can inhibit the oxidation of developers. However, 1-phenyl-3-methyl-5-pyrazolone also penetrates hair and functions as a coupler, forming a pink color upon reaction with p-phenylenediamine (PPD) or its analogs. The use of 1-phenyl-3-methyl-5-pyrazolone as an antioxidant would therefore require reformulation of colorant compositions in order to offset the color change in hair (hair color would shift to a redder hue). Hair colorant products are typically marketed in multiple different shades (sometimes hundreds of different shades), the use of 1-phenyl-3-methyl-5-pyrazolone as an antioxidant may require widespread reformulation, which is undesirable. As such, previous attempts to inhibit the oxidation of developers outside of the hair and inhibit color formation outside of the hair, e.g., using 1-phenyl-3-methyl-5-pyrazolone, have not been successful.
The pyrazol-5-one compounds of the invention inhibit the oxidation of developers outside of the hair and thereby inhibit color formation outside of the hair, without significantly altering the color inside the hair. The use of these compounds, therefore, does not require reformulation of colorant compositions to offset the color shift of the hair as that found when using 1-phenyl-3-methyl-5-pyrazolone.